Abstract
Of the 12 specimens of Calathus-like sphodrine beetles presently known from Baltic and Rovno amber deposits, 11 specimens were investigated using light microscopy, micro-CT scanning, and 3D imaging techniques. For the first time, many significant diagnostic characters of the external morphology and male and female genitalia of Eocene Sphodrini were studied in detail. Based on these data, three fossil species are diagnosed and placed in a natural group characterized by a derived pattern in elytral chaetotaxy and microsculpture and therefore the genus Quasicalathus Schmidt & Will, gen. nov. is described to comprise these species. Due to the presence of a styloid right paramere, Quasicalathus gen. nov. is considered a member of the sphodrine “P clade” of Ruiz et al. (2009). However, given the absence of synapomorphies of any species group of the P clade, the systematic position of Quasicalathus gen. nov. within this clade remains unresolved. The Baltic amber species Calathus elpis Ortuño & Arillo, 2009 is redescribed based on additional, fossil, non-holotype material and transferred to Quasicalathus gen. nov. Identification of the additional C. elpis fossil material remains slightly uncertain due to the non-availability of the holotype for direct comparison coupled with doubts regarding the accuracy of certain character states presented in its original description. Two species are newly described: Quasicalathus agonicollis Schmidt & Will, sp. nov., from Baltic amber, and Q. conservans Schmidt & Will, sp. nov., from Rovno amber.
Highlights
Beetles of the tribe Sphodrini Laporte, 1834 are known from Eocene fossil deposits only as species in the genus Calathus Bonelli, 1810 of the subtribe Calathina Laporte, 1834
The ten sphodrine specimens from Baltic amber available for us to study, belong to at least two different species of Quasicalathus, and all but one of the diagnostic characters we found to be relevant for these species are absent in the description presented by Ortuño and Arillo (2009)
In the specimen GZG 16188, the pattern of head microsculpture is quite differently developed from that what we found in Q. elpis and the below described Q. conservans sp. nov., this character state is unknown for the Q. agonicollis sp. nov. holotype
Summary
Beetles of the tribe Sphodrini Laporte, 1834 are known from Eocene fossil deposits only as species in the genus Calathus Bonelli, 1810 of the subtribe Calathina Laporte, 1834. Occurrence of Calathus fossils in Eocene Baltic amber (50–35 Ma; Standke 2008) was first noted by Handlirsch (1908), Klebs (1910), and later listed in several amber catalogues (e.g., Bachofen-Echt 1949, Larsson 1978, Spahr 1981). The subtribe Calathina of the tribe Sphodrini is a moderately diverse carabid beetle group comprising 173 species distributed in the Holarctic region. The bulk of the species (152) occurs in the Palearctic, 21 species in the Nearctic, and at least 31 endemic species are known to have an extralimital distribution in the Ethiopian. The majority of Calathina species are currently placed in the genus Calathus Bonelli, 1810.
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